linux-kernel - [PATCH] kvm: x86: correct the misleading comment in vmx_handle_external

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Date:   Mon, 10 Oct 2016 08:23:43 +0800
From:   "Longpeng(Mike)" <longpeng2@...wei.com>
To:     <pbonzini@...hat.com>, <rkrcmar@...hat.com>, <tglx@...utronix.de>,
        <mingo@...hat.com>, <hpa@...or.com>, <x86@...nel.org>
CC:     <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <zhaoshenglong@...wei.com>, <richard.weiyang@...wei.com>,
        "Longpeng(Mike)" <longpeng2@...wei.com>
Subject: [PATCH] kvm: x86: correct the misleading comment in vmx_handle_external_intr

Since Paolo has removed irq-enable-operation in vmx_handle_external_intr
(KVM: x86: use guest_exit_irqoff), the original comment about the IF bit
in rflags is incorrect now.

Signed-off-by: Longpeng(Mike) <longpeng2@...wei.com>
---
 arch/x86/kvm/vmx.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index cf1b16d..9fa3c76 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -8647,9 +8647,12 @@ static void vmx_handle_external_intr(struct kvm_vcpu *vcpu)
 	register void *__sp asm(_ASM_SP);
 
 	/*
-	 * If external interrupt exists, IF bit is set in rflags/eflags on the
-	 * interrupt stack frame, and interrupt will be enabled on a return
-	 * from interrupt handler.
+	 * If external interrupt exists, fakes an interrupt stack and jump to
+	 * idt table to let real handler to handle it. Because most of bits in
+	 * rflags are cleared when VM exit(Intel SDM volum 3, chapter 27.5.3),
+	 * the IF bit is 0 in rflags on the interrupt stack frame, so interrupt
+	 * is still disabled when return from the irq handler, but it will be
+	 * enabled later by the caller.
 	 */
 	if ((exit_intr_info & (INTR_INFO_VALID_MASK | INTR_INFO_INTR_TYPE_MASK))
 			== (INTR_INFO_VALID_MASK | INTR_TYPE_EXT_INTR)) {
-- 
2.7.4